1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a printing press with a plate cylinder carrying at least two printing plates.
2. Background Information
Printing presses may print a continuous web of material, such as paper. A plate cylinder of the printing press may firmly hold or lock-up a flat printing plate, for example a lithographic printing plate. An image to be printed is formed by ink which is transferred from the printing plate to the paper. In offset printing presses the plate first transfers ink to a blanket and then to the paper.
U.S. Pat. No. 5,284,093 purports to disclose a single-plate plate cylinder with a lock-up mechanism permitting fastening of the single plate.
U.S. Pat. No. 5,678,487 purports to disclose a lock-up mechanism used in conjunction with a tucker bar for fastening a single plate to a single-plate plate cylinder.
These patents however do not address the needs for large newspaper and other presses, where it may be desirable to have more than one printing plate spaced axially about the plate cylinder.
With such presses, each printing plate should able to be registered axially, i.e. positioned properly with respect to the plate cylinder and to each of the other printing plates. The single-plate cylinder devices described in the patents above may register the plate by moving the plate cylinder with respect to the printed material, and thus do not address the problem of independent registration.
In addition, the above-identified patents do not permit for independent plate removal on a multi-plate cylinder.
An object of the present invention is to provide a printing press having a multi-plate plate cylinder which permits for independent removal of each printing plate while the other printing plates remain attached. Another alternate or additional object of the present invention is to provide a printing press with a multi-plate cylinder which permits independent registration of each plate. Yet another alternate or additional object of the present invention is to provide a simple method for providing printing plates to a multi-plate plate cylinder.
The present invention provides a printing press comprising a multi-plate plate cylinder for carrying at least a first printing plate and a second printing plate, the plate cylinder having a cylinder body with an outer surface and a lock-up bar having a retracted position and an extended position, the lock-up bar extending radially beyond the outer surface in the extended position, the lock-up bar for fastening both of the first and second plates about the outer surface in the retracted position. The press also comprises a tucker bar adjacent the lock-up bar, the tucker bar including at least a first segment for tucking and holding the first printing plate on the plate cylinder and a second segment for tucking and holding the second printing plate on the plate cylinder, the first segment being independently movable with respect to the second segment.
By providing a segmented tucker bar with independently movable segments, a single plate of the multi-plate cylinder can be removed when a segment of the tucker bar is retracted. The other plates can remain held by the other segments, which can be in a plate retention position. Thus a single lock-up bar mechanism can be provided for the plate cylinder, which reduces the complexity and cost of the multi-plate plate cylinder, and yet the plates can still be independently removed.
Preferably, the plate cylinder includes at least one register pin associated with each printing plate, so that the printing plate can be properly registered in an axial direction. The present invention, by permitting each plate to be removed thus permitting the register pins to be adjusted, advantageously permits independent registration of each plate.
Advantageously, the pins can be manually adjustable from outside the cylinder when the lock-up bar is in the extended position.
The plate cylinder also advantageously may include at least one spring element for clamping a lead and/or trail end of a printing plate.
The tucker bar may include a plurality of independently-actuable pistons for moving the different segments. The tucker bar preferably acts on a trail end of a printing plate, which is held on the lock up bar. The lead end of the printing plate preferably is held on the plate cylinder body.
The present invention also provides a method for removing printing plates from a multi-plate plate cylinder having a common lock-up bar with a retracted position and an extended position, the plate cylinder for carrying at least a first printing plate and a second printing plate, the method comprising the steps of:
contacting the first printing plate with an associated first segment of a tucker bar when the common lock-up bar is in an extended position, while the second printing plate is not contacted by an associated second segment of the tucker bar;
moving the common lock-up bar to the retracted, i.e. locking, position so that the first printing plate is fastened and so that an end of the second printing plate is free; and
removing the second printing plate from the plate cylinder.
By providing contact to the first printing plate even while the lock-up bar is in the extended position, the first printing plate does not need to release from the plate cylinder. Thus the second printing plate can be removed independently of the first printing plate cylinder, even with a common lock-up bar for both plates.
The present method can further include moving all segments of the tucker bar away from the cylinder surface after the moving of the common lock-up bar step.
The removing step can include rotating the plate cylinder approximately one revolution. A second end of the second printing plate opposite the free end can then be removed. The removal of the second end can be aided by returning the first segment to contact the first printing plate and extending the lock-up bar.
If desired, a register pin associated with the second plate may then be adjusted manually, for example by sliding the register pin axially.
While the first segment holds the first printing plate, a new or the same second printing plate may then be attached to the plate cylinder. The second plate may be attached by inserting a lead edge of the printing plate into a slot formed in the periphery of the plate cylinder. The lead edge can be tucked into the slot with the second segment, and the lock-up bar can be moved to its retracted position, locking the second printing plate lead edge and the first printing plate. All segments of the tucking bar are then moved away from the cylinder and the cylinder is rotated about one revolution so that the new second plate wraps around the cylinder. The lock-up bar is then moved to the extended position, with the tucker bar segment associated with the first printing plate holding the first printing plate in place. The second segment then tucks the trail end of the second plate so the trail end is held by the lock-up bar, which is then retracted. Both the first and second plates are thus firmly held. All segments of the tucker bar are then moved away and the printing press is ready for operation with a new or newly-registered second plate.
Preferably, four plates are carried by the plate cylinder, with each plate being independently replaceable. If, for example, the second plate is to be replaced, the third and fourth plates are held in a similar manner to the first plate.